Knowra Isotonic solution Isotonic solution Two solutions are isotonic when they exert equal osmotic pressure across a specified semipermeable membrane, causing no net solvent movement between them.
Osmosis : The net movement of solvent across a selectively permeable membrane toward the side with greater effective solute concentration. Equal osmotic pressures balance the solvent flow that osmosis would otherwise produce.
Normal saline : A 0.9% sodium chloride solution commonly used as an intravenous fluid. It is conventionally described as isotonic to blood, though its physiological effects depend on context.
Hypotonic solution : A solution with lower effective solute concentration than its comparator, tending to drive water into cells. Unlike an isotonic solution, it causes net water entry into cells when membrane conditions permit.
Diffusion : The net spread of particles from regions of higher concentration to regions of lower concentration. Solute diffusion and solvent osmosis are distinct processes that can occur across the same membrane.
Osmotic pressure : The pressure required to stop solvent from crossing a semipermeable membrane into a solution. Isotonic solutions have equal osmotic pressures across the specified membrane.
Ringer's lactate : An intravenous crystalloid solution containing sodium, chloride, potassium, calcium, and lactate. Its electrolyte composition and approximate isotonicity make it a common fluid for volume replacement.
Hypertonic solution : A solution with higher effective solute concentration than its comparator, tending to draw water out of cells. Unlike an isotonic solution, it causes net water loss from cells when membrane conditions permit.
Solvent : A substance that dissolves one or more solutes to form a solution. In biological isotonicity, water is usually the solvent whose net movement is considered.
Semipermeable membrane : A barrier that permits some substances to pass while restricting others. Which solutes cross this barrier determines whether they contribute to tonicity.
Red blood cell : A blood cell that carries oxygen using hemoglobin and changes volume with water movement across its membrane. Its stable volume in an isotonic medium demonstrates balanced water exchange.
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